same note, different accidentals

[Lasse Rempe]

Hello ---

I have only recently started using LilyPond, so this may be a newbie question,
but I didn't find a solution anywhere.

I am typesetting a piece where, on the same beat, one voice has a b, while the
other has a b flat. Even when I use the NoteColumn property to separate the
stems, LilyPond insists on only setting one accidental, which of course is not
going to work ...

Of course I could write the b flat as an a sharp (and since it's a piano part,
it doesn't make a difference), but that doesn't seem quite satisfactory.